Everybody agrees or likes Canon's 70-200mm series of lenses.
well, true but it is a very basic bread and butter kinda lens , so for me it is not so spcieal as I can call it a magic.
so , for me it has to be the 85LMKII or the 24LMKII.
oh for me , the 17-55f2.8IS was a magic but I cannot use it on my 5D2.
Beyond that, it is a lot of preference.
Some lenses that get good praise are the 17-55 IS, 24-105mm L, 24-70mm 2.8L,
all the macro lenses. A few others that get some great votes and may fans. but I can honestly say only the 70-200mm series is the only lens I have read on for almost any brand that nobody says is bad.
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Darkness is the monster and your shutter is your sword, aperture your shield and iso your armor. Strike fast with your sword and defend well with your shield and hope your armor holds up.
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Ken.